260 3=G. C. Crick—Gigantic Cephalopod Mandible. 
Messrs. Fergusson and Bateman,’ as a result of their recent 
researches on greisenization from different localities, have come to 
the general conclusion that in the chemical changes involved there 
is an increase in silica, aluminium (which is only in part Al, O.), 
and probably of iron oxides, a loss of lime, magnesia, and the alkalies, 
the losses of the alkalies being approximately in proportion to the 
amount of each originally present, and only in slight degree selective. 
The following figures, extracted from analyses of granite and greisens, 
are instructive. In the cases of veins, the granite country rock would 
probably, however, be less acid than the former before greisenization. 
NEw SouTH WALES.2 ERZGEBIRGE.® GUNONG BAKAU, MATLAYA. 
Grei Grei Grei é Grei < 
Unaltered eae Hous a Unaltered Caney pees Unaltered (quakes: aoe 
Granite. | from vein | Granite. | mica, oe a ‘| Granite. | mica, os aay 
vein. wall, topaz), | 0P42/. topaz), | 0P22)- 
SiOg .| 76:69 | 75-42) 78-47| 74-68 | 70-41] 79-73 | 77-12 | 77-50 | 80-08 
AlgO3 .| 10-89 | 12-98] 11-50] 12-73 | 13-06") 10-244 11-07 | 13-01 | 12-45 
Fee O3 0:76 1:68 | 2-64 — 1-42 \ Air75) | “015 N05 
FeO, 0-39 | 0-58] 1-05] 3-00 | 5-09 j Te ae 
etc. 
CoNncLusIon. 
The topaz-bearing rocks of Gunong Bakau bear striking similarities 
in their mode of occurrence and mineral content to those found 
in other tin-fields, and especially to those of Erzgebirge. The. 
topaz and cassiterite in the latter tin-field have been proved to be of 
secondary origin, and the evidence appears to be very strong for 
presuming that these minerals are also of secondary origin at Gunong 
Bakau. 
V.—Norr on a eigantic CepHaLopop MANDIBLE. 
By G. C. Crick, F.G.S., F.Z.S., of the British Museum (Natural History). 
[Published by permission of the Trustees of the British Museum. ] 
[{\HE British Museum has recently received (in the James W- 
Butler collection, presented by his daughter, Miss Daisy Butler) 
a particularly fine mandible of a gigantic fossil Cephalopod.® 
Unfortunately the locality of the fossil is not recorded, but as the 
collection contained quite a number of specimens from Bradford 
Abbas (Dorset) and the immediate neighbourhood, and the matrix 
of this specimen agrees very closely with that of those examples, 
there can be little doubt that the locality of the fossil is almost 
1 H. C. Fergusson & A. M. Bateman, ‘‘ Geologic Features of Tin Deposits ’’ : 
Heonomic Geology, vol. vii, pp. 250-1, 1912. 
2 Tbid.,;'p: 241. 
3 Tbid., p. 237. 
* After deduction of part of Al, which formed 7-86 and 7-57 per cent of 
these rocks. 
> Calculated as Fee Os. 
5 British Museum (Natural History), Geol. Dept., reg. No. C. 18659. 
